1. Field of the Invention
The present invention relates to an image display device for displaying an image on a display member by irradiation with electrons emitted from an electron source.
2. Related Background Art
Conventionally, two types of electron-emitting devices electron sources, hot cathode devices and cold cathode devices, are known. Examples of the cold cathode device include a surface conduction electron-emitting device, a field emission (hereinafter referred to as FE) electron-emitting device, a metal/insulating-layer/metal (hereinafter referred to as MIM) electron-emitting device. Application of these devices to, for example, an image display device, an image-forming apparatus such as an image-recording apparatus and a charged beam source has been studied.
In particular, as an application example of a surface conduction electron-emitting device to an image display device, an image display device that combines to use surface conduction electron-emitting devices and phosphors for emitting light by irradiation of electron beams has been studied as disclosed in U.S. Pat. No. 5,066,883 and Japanese Patent Application Laid-open Nos. 2-257551 and 4-28137 filed by the applicant of the present application. The image display device that combines to use surface conduction electron-emitting devices and phosphors is expected to have a property that is more excellent than that of conventional image display devices of other systems. For example, it is more excellent than a liquid crystal display device, which has been widely used in recent years, in that it does not need a back light because it is a self-luminescence type and that it has a wider view angle.
In addition, a method in which a number of FE electron-emitting devices are arranged to be driven is disclosed, for example, in U.S. Pat. No. 4,904,895 by the applicant of the present application. In addition, as an example in which an FE electron-emitting device is applied to an image display device, for example, a flat panel display reported by R. Meyer et al. is known (R. Meyer: xe2x80x9cRecent Development on Microtips Display at LETIxe2x80x9d, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)).
Among the image display devices using electron-emitting devices as described above, a thin plane type display device is attracting attention as a display device replacing a cathode-ray tube display device because it occupies less space and is light in weight.
FIG. 17 is a perspective view showing an example of a display panel portion forming a plane type image display device, which is shown with a part of the panel cut away in order to show an internal structure.
In the figure, reference numeral 3115 denotes a rear plate, 3116 denotes a side wall and 3117 denotes a face plate. The rear plate 3115, the side wall 3116 and the face plate 3117 form an envelope (an airtight container) for maintaining a vacuum inside the display panel.
A substrate 3111 is fixed to the rear plate 3115, and Nxc3x97M cold cathode devices 3112 are formed on this substrate 3111 (N and M are positive integers equal to or larger than two and are properly set according to the target number of display pixels). In addition, as shown in FIG. 17 the Nxc3x97M cold cathode devices 3112 are wired by M lines of row-directional wiring 3113 and N lines of the column-directional wiring 3114. A portion composed of the substrate 3111, the cold cathode device 3112, the row-directional wiring 3113 and the column-directional wiring 3114 is called a multi-electron beam source. In addition, an insulating layer (not shown) is formed between both the wiring at least in parts where the row-directional wiring 3113 and the column-directional wiring 3114 cross each other, whereby electrical insulation is maintained.
A fluorescent film 3118 consisting of a phosphor is formed on the lower surface of the face plate 3117, and the phosphors of three primary colors of red (R), green (G) and blue (B) (not shown) are arranged. An example of the phosphors is shown in FIG. 14. Here, a portion surrounded by dotted lines is referred to as a sub-pixel and a portion surrounded by solid lines is referred to as a pixel. One pixel is composed of three sub-pixels consisting of R, G and B. In addition, a black body (not shown) is provided among the above-mentioned phosphors forming the fluorescent film 3118. Moreover, a metal back 3119 made of Al or the like is formed on the surface on the rear plate 3115 side of the fluorescent film 3118.
Dx1 to Dxm, Dy1 to Dyn and Hv are terminals for electric connection of an airtight structure provided for electrically connecting the display panel and electric circuit (not-shown). Dx1 to Dxm, Dy1 to Dyn and Hv are electrically connected to the row-directional wiring 3113 of the multi-electron beam source, the column-directional wiring 3114 of the multi-electron beam source and the metal back 3119, respectively.
In addition, a vacuum in the order of 133xc3x9710xe2x88x926 Pa (10xe2x88x926 Torr) is maintained inside the above-mentioned airtight container.
FIG. 18 shows a schematic view of an electron beam spot shape and an amount of electron beams when electron beams emitted from a surface conduction electron-emitting device have collided against a phosphor (not shown) on the face plate 3117.
In the image display device using the above-described display panel, when a voltage is applied to each cold cathode device 3112 through the terminals Dx1 to Dxm and Dy1 to Dyn which are arranged outside the container, an electron is emitted from each cold cathode device 3112. At the same time, a high voltage of several hundreds of V to several kV is applied to the metal back 3119 through the terminal Hv which is arranged outside the container, whereby the emitted electrons are accelerated and caused to collide against the internal surface of the face plate 3117. Consequently, the phosphors of each color forming the fluorescent film 3118 are excited to emit light and an image is displayed.
It has been found that the above-described display panel of the image display device has the following problems.
In a thin image display device, there is an upper limit to the high voltage that can be applied to a part between a rear plate and a face plate. Thus, it is absolutely necessary to increase the amount of current from electron-emitting devices in order to realize a desired light-emitting luminance, which causes Coulomb degradation of the phosphor. In particular, in the case of an electron emitting device in which emitted electrons have an initial velocity in a direction other than the direction of the electrode from the electron-emitting device toward the face plate as in the surface conduction electron-emitting device as shown in FIG. 18, there is a deviation in the current density distribution, which makes the degradation of a phosphor more serious (a horizontal FE of FIG. 19 (FE provided with both an emitter and a gate on the surface of a substrate) is also a device having the same problem). That is, since an amount of electron applied to one sub-pixel in order to realize desired luminance concentrates in one part within the one sub-pixel, the degradation of the phosphor in that part is aggravated rapidly and, as a result, the life of the phosphor is rendered short.
Thus, we have found that it is effective to disperse and arrange electron-emitting areas of electron-emitting devices (one unit) forming one sub-pixel in a plurality of places in order to eliminate the deviation of the current density distribution and, as a result, prevent progress of partial degradation of the phosphor. If two electron-emitting areas are provided, it becomes possible to reduce the amount of current from one of the electron-emitting areas by fifty percent and the concentration of the current density is improved by approximately fifty percent as long as the luminance thereof are equivalent. Thus, it becomes possible to increase the life of the phosphor so as to be twice as long as that in the conventional display panel of the image display device. We have found anew that it is possible to prevent degradation of the phosphor with such a structure.
Note that, such a structure involves a problem in the size of an electron beam spot and its accessible position as compared with the structure in which electron-emitting areas are not dispersed and arranged in a plurality of places. As measures for coping with problems due to the size of an electron beam spot and its accessible position, an attempt has been made to solve such problems by separately providing an electrode for shaping a beam as described in Japanese Patent Application Laid-open No. 3-263742 or by controlling the overlapping degree of beams in terms of the distances between a plurality of electron-emitting areas as described in Japanese Patent Application Laid-open No. 7-235256. However, in the cases of the technologies disclosed in these patent applications, there still are problems. In Japanese Patent Application Laid-open No. 3-263742, the structure of a display device is made rather complicated and manufacturing of the display device is difficult because an electrode for shaping a beam is provided. In addition, in Japanese Patent Application Laid-open No. 7-235256, a sufficient space is required for providing electron-emitting devices on a rear plate in order to realize desired intervals between electron-emitting areas and the display device can not obtain sufficiently high definition. Thus, these problems should be solved for a practical use.
In addition, in these Japanese patent applications, as too much importance is placed on the improvement in terms of the size of a beam spot; thus, if electron beams are focused excessively and a plurality of electron beams overlap each other excessively, deviation of a current density may be more obvious. In such a case, the problem of degradation of the phosphor may be more serious.
The present invention has been made in view of the above, and an object of the present invention is therefore to provide an image display device which makes it possible to prevent degradation of a phosphor and to realize high definition with a simple structure.
According to the present invention, there is provided an image display device comprising an electron source and a display member for displaying an image by irradiation with electrons emitted from the electron source, characterized in that the electron source has a plurality of units provided with a higher voltage electrode disposed on a substrate, lower voltage electrodes provided in parallel on both sides of the higher voltage electrode across the voltage electrode and electron-emitting areas located between the lower voltage electrodes and the higher voltage electrode, electron beams emitted from each of the electron-emitting areas in each unit cross with each other, and an equipotential surface to be formed between the substrate and the display member has an area protruding to the display member side on the higher voltage electrode.
Further, according to the present invention, there is provided an image display device comprising an electron source and a display member for displaying an image by irradiation with electrons emitted from the electron source, characterized in that the electron source has a plurality of units provided with a higher voltage device electrode disposed on a substrate, lower voltage device electrodes provided in parallel on both sides of the higher voltage device electrode across the higher voltage device electrode, electron-emitting areas located between the lower voltage device electrodes and the higher voltage device electrode and a wiring electrode connected to and disposed on the higher voltage device electrode, electron beams emitted from each of the electron-emitting areas in each unit cross with each other, and an equipotential surface to be formed between the substrate and the display member has an area protruding to the display member side on the wiring electrode.